After finding and downloading a module, the next step would be to copy it the modules folder. Most people copy the file to the default modules folder here http://sitename.com/drupal/modules this is where all the modules that ship with Drupal are stored so it seems somewhat logical to do this. But this folder is actually meant to store only Drupal's default modules. Instead you should go to http://sitename.com/drupal/sites/all folder, there you will see a readme.txt file. This file will clearly tell you the trick. You just need to create a new folder named modules here. Now copy the modules folder here. That's all, you have successfully installed the module.

Next step would be to enable the module through the Admin interface. To do this navigate to Administer » Site Building » Modules. Here you will see a list off all installed modules, and our newly installed module will also be listed here. You just have to check the enable check box against the new module and then click the Save Configuration button. That's all.